In my opinion it's the least useful magic school, because of few adventure spells (only Visions, which belongs to all schools anyway) and also few useful combat spells.
Berserk is probably the best fire spell and it really is strong, but some creatures are immune to it, it can be resisted, different artifacts protect against it and it only lasts for one action.
Blind is also good, but you don't really need Fire Magic for it.
Then there are all the damage spells, Fire Wall, Fireball, Land Mine, Inferno and Armageddon, and even though I boosted the damage of all these spells (except Armageddon) and I do sometimes cast them, you don't really need Fire Magic for them either, especially if you have the Earth or Air Orb instead.
Then there is Curse and Bloodlust which can be okay sometimes, but I much prefer Slow/Haste.
Frenzy is situational, but can be useful with Devils.
Slayer I made into a mass spell, but it's still very situational.
Sacrifice is good, but I never use it because Resurrection/Animate Dead is usually enough.
Fire Elemental is actually my most prefered elemental to summon, since it's faster than Earth, but also pretty tough. But summoning elementals is also a rarity for me.

Overall I usually end up quite disappointed in Fire Magic, but what do you think about it?

Mass Blind, was that ever considered?, that would be completely game breaking.

@OhforfSake Good point and I like Fire Magic too, most of the time it just feels unnecessary to me.
If Fire Magic became better AI would benefit from it as well.
I don't know what could make it better though, maybe a brand new adventure spell or Visions belonging only to Fire Magic. I also wish Land Mines would stop the enemy, at least for that round. Land Mine feels completely useless to me, Quicksand is much better and cheaper.
I guess Misfortune could give -3 instead, but I probably would'nt feel like casting it anyway. Fire Shield could also become a mass spell, but I'm not sure if that would be OP.

I think it's fairly potent. Many poeple share your opinion just because it does not provide instant benefits, like Implosion or Prayer, let's stay. But take a look at a few spells:
Bloodlust, Curse, Blind, Armageddon, Berserk, Frenzy and Slayer are all fairly potent and strong spells that can change the outcome of a battle.

Erdamon said:
Bloodlust, Curse, Blind, Armageddon, Berserk, Frenzy and Slayer are all fairly potent and strong spells that can change the outcome of a battle.

Blind and Armageddon are almost just as good without Fire Magic.
And yeah you have a point of Fire Magic not being instantly rewarding.
Bloodlust is okay, but I prefer Bless.
About Curse, enemy might resist it, be immune to it or it might counter with Mass Bless instead.
Frenzy is dangerous, because you lose all defense, so you need to be careful about it.
Slayer just affects few creatures, so it rarely has much effect. (Master Genies might cast it after enemys level 7 units are gone.)
Berserk is awesome, when it works, this is the primary reason for picking Fire Magic.

Is useless, because the whole system was corrupted by mass slow/haste + the enormous lack of balance between might and magic heroes. However berserk is looking like a cheat to me so I never used it, even in maps which required its use, I tried to work around with a more pleasant way.

Mass blind should have been a reward for high level mages and then only countered by mass cure - the unit being hit gets its turn instantly, if it does not die entirely - but then they removed access to water magic to barbs, so the whole thing is a mess to rearrange.

If you have enough mana, wouldnt mass-blind end the battle instantly? You'd just keep casting it till you wipe the enemy out, mass-cure wouldnt be a solution because the blinded opponent wont get a turn to cast it.
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i challenge ANYONE to prove me wrong. you CANNOT. -fred

artu said:If you have enough mana, wouldnt mass-blind end the battle instantly? You'd just keep casting it till you wipe the enemy out, mass-cure wouldnt be a solution because the blinded opponent wont get a turn to cast it.

Thats why I added the condition of instant act if one of the blinded stack is hit. Mass blind/you hit one blind unit/that unit gets instantly turn if not killed entirely, thus giving opportunity to mass heal.

The paradox in the "heroes of Might and Magic" is that a 99 - all skills - mage is in no way stronger than the same 99 all skills barb, when it comes to casting (save for a pitiful +15% if sorcery - offense gives +30% for all stacks, on the other side). This is what kills the diversity, although it can be created within WoG ideas. Magic heroes should get access to advanced spells features, as mass fire shield, mass blind, mass force fields, mass land mines etc.

I have never used Berserk, but I started using Berserk in HotA, because AI uses Berserk. Fire is very powerful, for example, Curse versus Haste. Piece of cake! But Fire versus Earth is more difficult if there is Water skill. That's why Cure is powerful, when Faerie Dragon needs Cure or Anti-Magic. Otherwise everything is good, and for professional use Sacrifice. So the fire belongs to the evil magician. Rampart doesn't have Fire skill, it's not true, yes the skill distributor sometimes gives Fire skill, but the skill can't be study or buy. So very strong is Sacrifice with also Diplomacy. Strategist! My guy uses Air and Fire, for Blind and Haste. So expert Blind is very powerful when no need to use a Resurrection, if the monster is a legion. It is also the best strategy, for multiplayer.
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Fight MWMs - stand teach

I personally enjoy Fire Magic quite a bit.
As already pointed out it may not be as dominant as Earth/Air Magic but I still believe it has several game changing spells like Berserk, Sacrifice and Armageddon. If one can manage to acquire one of these, the outcome can quickly be turned into one's favor.
Also using mass Curse vs Dungeon is amusing minding the large damage range of their lv 1, 2, 3, 5, and 6 creatures.

Once your hero reaches a spell power of 12+ the Fireball Spell can literally incinerate any unit at its initial impact hex before expanding itself a whole 4 x 4 radius and, decimates the enemy's troops in one single spell cast of it.

I truly believe that it is way too exploited in Heroes 5: Wizard faction, again.

LucPatenaude said:... before expanding itself a whole 4 x 4 radius and, decimates the enemy's troops in one single spell cast of it.

Fireball only covers 7 hexes: the target hex and the 6 hexes directly in a circle around it. What are you even talking about? ____________
The last Reasonable Steward of Good Game Design and a Responsible Hero of HC. - Verriker

i've always found fireball to be pretty weak; even inferno. but maybe that's just me. if i have a choice, i'll go for air or earth magic before i'll ever go for fire magic. i've just never found it to be particularly potent or worthwhile.

Curse - excellent level 1 spell, good vs stronghold, dungeon, inferno
Blind - obvious, expert blind, no retalition.
Fireball and Inferno - weak but they are good against low level creatures or in campaigns
Frenzy - excelent vs high defense creatures or heroes with lots of defense skill.
Berserk - combining with Armor of the Damned and fast creature against opponent, game changer. with some tricks it is possible to use berserk on all 7 enemy stacks.
Armageddon - powerful, best combined with Phoenixes and Efreets(both can resurected). Insane damage with Sorcery specialist + fire orb cheaper then implosion and better then chain lighting.

Sacrifice - if you are low sp and mana it can help save your best unit, because it ressuct stronger then level 4 ressurection.